There is a growing body of both experimental data to suggest that chronic inflammation of the colon is associated with enhanced production of nitric oxide(NO). Nitric oxide is thought to play an important role in modulating the inflammatory by virtue of its ability to affect blood flow and leukocyte function. Furthermore, this reactive nitrogen intermediate will rapidly and spontaneously interact with molecular oxygen or superoxide to yield potentially injurious oxidizing and nitrosating agents. Although the sources of this enhanced NO production in vivo have not been identified, it is very probable that the phagocytic leukocytes (neutrophils, monocytes, macrophages), known to accumulate within the colonic interstitium, as well as cytokine-activated colonic epithelial cells represent the major sources of this reactive metabolite of nitrogen. We have demonstrated that extravasated neutrophils (PMNs) and macrophages as well as cytokine-activated epithelial cells produce large amounts of NO. The overall objective of this proposal is to better understand the role that NO and/or NO-derived metabolites may play in chronic colonic inflammation. Our central hypothesis is that leukocyte and possibly epithelial cell-derived NO mediates the mucosal injury and dysfunction associated with chronic colitis. In order to test this hypothesis we propose the following specific aims: 1) We will assess the role that NO or NO-derived metabolites may play in mediating the mucosal injury and inflammation observed in a model of chronic granulomatous colitis in rats, 2) We will quantify both the messenger RNA and enzymatic activity of the inducible form of nitric oxide synthase within the colonic mucosa during acute and chronic granulomatous inflammation, 3) We will determine whether the overproduction of endogenous and/or exogenous NO injuries cultured intestinal epithelial cells in vitro, and 4) We will investigate the potential role that NO may play in mediating the hyperemia associated with acute and chronic colonic inflammation. Data obtained in these studies should provide new information regarding the role of NO as s mediator injury and inflammation in a model of colonic granulomatous colitis.